The focal length of the D415's left and right imagers is 1.88 mm. The color sensor's focal length is 1.93 mm. In the RealSense SDK 2.0 software, the focal length is described by fx and fy as a multiple of pixel width and height.
I do not have data on the cx and cy of the camera. The 400 Series' dynamic calibration guide describes the principal point in terms of px and py
"Principal point - specified as [px; py] in pixels for left, right, and RGB cameras"
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Marty is right about the information he has shared with you. In the following link you will find the Intel® RealSense™ Depth Module D400 Series Software Calibration Tool, this guide specifies how to change the calibration.
Hope this helps to clarify your question.